The present invention relates to rotary fluid pressure devices used as hydraulic motors, and more particularly, to such motors in which the fluid displacement mechanism is a gerotor gear set, and the motor valving is of the spool valve type.
Rotary fluid pressure devices which include a gerotor gear set as the fluid displacement mechanism are typically used as low-speed, high-torque motors. Such gerotor motors have traditionally been classified as being either of the "spool valve" type, or of the "disk valve" type. In a spool valve gerotor motor, the valving is accomplished at a cylindrical interface between a spool valve and a spool bore defined by the surrounding housing. In a disk valve type, the valving is accomplished at a flat, transverse, planar interface of a disk valve and a stationary valve member.
Although the present invention may be included in a gerotor type device being utilized as a pump, it is especially adapted for use in a low-speed, high-torque gerotor motor, and will be described in connection therewith.
For many years, some of the gerotor motors made and sold commercially, both by the assignee of the present invention as well as by others, have had the motor valving disposed "rearwardly" of the gerotor gear set, and this has been true especially in regard to disk valve type motors. In more recent times, the assignee of the present invention has begun to commercialize motors having the spool valve disposed rearwardly (i.e., opposite the output end) of the gerotor gear set.
In many vehicle applications for low-speed, high-torque gerotor motors, it is desirable for the motor to have some sort of parking brake or parking lock, and in certain vehicle applications, it is desirable for the motor to have some sort of dynamic brake which can be applied while the vehicle is still moving, to bring the vehicle to a stop. It should be understood that, as used herein, the term "dynamic" brake means a brake having dynamic capabilities, i.e., one which can begin to be applied while the vehicle is still moving, but "dynamic" does not mean a true service-type brake which would be applied when the vehicle is traveling at its normal operating speed.
For many years, those skilled in the art have attempted to incorporate brake and lock devices into gerotor motors. Examples of such devices are illustrated and described in U.S. Pat. Nos. 3,616,882 and 4,981,423. In the device of U.S. Pat. No. 3,616,882, a braking element is disposed adjacent the forward end of the gerotor star, and is biased by fluid pressure into frictional engagement therewith. Such an arrangement involves a certain degree of unpredictability of performance, in view of variations in clearances, etc. Such an arrangement also requires a substantial redesign of the wear plate and forward bearing housing of the motor.
In the device of U.S. Pat. No. 4,981,423, there is a multi-disc brake assembly which is of the "spring-applied, pressure-release" type. The arrangement of U.S. Pat. No. 4,981,423 also requires almost total redesign of the forward bearing housing, and also results in a much larger bearing housing. In addition, the disc pack is in splined engagement with the output shaft and, therefore, must be able to brake or hold the full output torque of the motor, thus necessitating that the discs, the spring, and the apply/release piston all be relatively larger than is desirable. A related problem is that such a brake arrangement can reduce certain of the performance ratings of the motor, such as the side load capacity of the output shaft, which is generally considered very undesirable by the OEM customer.